The present invention relates to a process for producing a sintered color pencil lead which can draw lines having excellent light fastness and weatherability while having a vivid coloring property and a sufficiently high density in drawn lines and is excellent in a mechanical strength such as a bending strength and which can readily be erased with an eraser and is particularly suited as a fine size color pencil lead for a mechanical pencil.
Conventional sintered color pencil leads are used for mechanical pencils in many cases, and a production process therefor includes a principal production process in which a blend composition comprising an filler such as boron nitride and a binder such as clay is kneaded, extruded and then subjected to heat treatment to prepare a porous lead and in which an ink comprising a dye is filled into pores of this lead.
However, since the colorant is a dye, the problem with the dye is that the stability with the passage of time such as light fastness is inferior. Further, if a lead has pores having a size at the level in which the pores can be impregnated with a pigment-dispersed ink, the lead is weak in strength and can not serve as a practical lead for a mechanical pencil.
The present applicant has heretofore filed Japanese Patent Application Laid-Open No. Hei 8-48931, Japanese Patent Application Laid-Open No. Hei 9-67540, Japanese Patent Application Laid-Open No. Hei 2000-17220 and Japanese Patent Application Laid-Open No. Hei 2000-17221 in connection with methods for obtaining a lead having a high strength. In all of these methods, obtained are sintered leads which can be impregnated with a pigment-dispersed ink so as to provide drawn lines with a high density and which is stronger in strength than the practical level applicable to a lead for a mechanical pencil. However, further desired is a sintered lead whose density in drawn lines thereof is further more improved and whose strength is further more than the practical level.
Further, the present inventors have filed Japanese Patent Application Laid-Open No. Hei 8-143810, Japanese Patent Application Laid-Open No. Hei 8-143811, Japanese Patent Application Laid-Open No. Hei 8-143812 and Japanese Patent Application Laid-Open No. Hei 8-259874 in connection with methods for producing organic pigments in pores of a porous lead for a mechanical pencil by chemical reaction. These methods have made it possible to impregnate pores of a lead having a small pore diameter with an organic pigment. However, problems with these methods are that, since the reaction is carried out in the presence of a strong acid or a strong base, the leads are liable to be a little deteriorated and that, since the production process is different according to each pigment, mixing color and producing multiple color are difficult.
An object of the present invention is to solve the defects of the sintered color pencil leads produced by the conventional techniques described above and further improve the prior art of the present inventors described above and to provide a process for producing a sintered color pencil lead which can draw lines having excellent light fastness and weatherability while having a vivid coloring property and a sufficiently high density in drawn lines and is excellent in a mechanical strength such as a bending strength and which can readily be erased with an eraser.
The present inventors have done intensive researches in order to solve the problems described above. As a result, they have found that the above problems can be solved by filling pores of a white or light-colored porous sintered lead with a specific compound and pigmenting the compound by heating, and thus they have come to complete the present invention.
That is, a process for producing a sintered color pencil lead characterized by forming a white or light-colored porous sintered pencil lead that is pigmented with an organic pigment by treating said porous sintered pencil lead with a solution of at least one compound of the following Formula (I) to be filled with said compound and then by forming said organic pigment within the pores by means of heating,
A(B)xxe2x80x83xe2x80x83(I)
in which x is an integer from 1 to 8,
A is the radical of a chromophore of the quinacridone, anthraquinone, perylene, indigo, quinophthalone, indanthrone, isoindolinone, isoindoline, dioxazine, azo series, phthalocyanine or diketopyrrolopyrrole which is attached to x groups B via one or more heteroatoms selected from the group consisting of N, O and S and forming part of the radical A,
B is hydrogen or a group of the formula 
where at least one group B is not hydrogen and, if x is 2 to 8, all the groups B can be identical or different, and L is any suitable solubilizing group.
To be more specific, pores of a white or light-colored porous sintered lead comprising a colorless or white filler and silicon nitride prepared from a starting material of perhydropolysilazane which is a binder may be filled with a solution prepared by dissolving the compound (I) described above in an organic solvent and pigmented by heating.
The embodiment of the present invention shall be explained below in detail.
A process for producing a sintered color pencil lead characterized by forming a white or light-colored porous sintered pencil lead that is pigmented with an organic pigment by treating said porous sintered pencil lead with a solution of at least one compound of the following Formula (I) to be filled with said compound and then by forming said organic pigment within the pores by means of heating,
A(B)xxe2x80x83xe2x80x83(I)
in which x is an integer from 1 to 8,
A is the radical of a chromophore of the quinacridone, anthraquinone, perylene, indigo, quinophthalone, indanthrone, isoindolinone, isoindoline, dioxazine, azo series, phthalocyanine or diketopyrrolopyrrole which is attached to x groups B via one or more heteroatoms selected from the group consisting of N, O and S and forming part of the radical A,
B is hydrogen or a group of the formula 
where at least one group B is not hydrogen and, if x is 2 to 8, all the groups B can be identical or different, and L is any suitable solubilizing group.
In a process for producing a sintered color pencil lead in accordance with the present invention, a white or light-colored porous sintered lead is formed and pores of the white or light-colored porous sintered lead are filled with a solution prepared by dissolving at least the compound (I) described above in an organic solvent and pigmented said compound in said pores by heating.
In the present invention, the porous sintered lead is formed from a colorless or white filler which is a publicly known substance, such as boron nitride, talc and mica and a binder such as silicon nitride, silica, alumina and zirconia and a solid solution thereof or clay. In particular, preferably suitable in terms of strength is a lead comprising a binder of silicon nitride prepared from perhydropolysilazane used as a starting material, which is disclosed in Japanese Patent Application Laid-Open No. Hei 8-48931.
The filler shall not specifically be restricted as long as it has heretofore been used as an filler for a sintered color pencil lead and is colorless or white, and any substances can be used. For example, the filler described above can be used, and it is a matter of course that a mixture of several kinds thereof can be used. Further, silica and alumina can be used as the filler depending on the kind and the sintering temperature of the binder.
A pore diameter of the porous color pencil lead used in the present invention shall not specifically be restricted as long as it can be impregnated with a solution prepared by dissolving the compound of Formula (I) in an organic solvent. However, a minimum value of the pore diameter is considered to be about 0.1 xcexcm, so that it is preferable to use those in which all pore diameters are 0.1 xcexcm or more. Taking a distribution of the pores into consideration, if the pores having a diameter falling in a range of smaller than 0.1 xcexcm are distributed in a large number, then the pores which can not be filled with a pigment increase to deteriorate the coloring property, and therefore it is preferable that the pores having a diameter of smaller than 0.1 xcexcm account for 40% or less, more preferable 20% or less based on the total volume.
Considering strength of the lead, the pore diameter has preferably a maximum value of 0.4 xcexcm or less.
Considering the coloring property onto a paper surface, the porosity distributing in a range of 0.1 xcexcm or more and 0.4 xcexcm or less, preferably 0.1 xcexcm or more and 0.3 xcexcm or less in the pore diameter of the porous pencil lead accounts for preferably 10 vol % or more, more preferably 15 vol % or more based on a volume of the lead.
In the present invention, the sintered color pencil lead is obtained by impregnating and filling the pores of the sintered lead described above with the compound of Formula (I) dissolved in an organic solvent and then heating the lead to convert the compound into an organic pigment.
The group A of the Formula (I) is a publicly known chromophore having a basic structure:
A(H)x
for example, a residue of compounds described below and all publicly known derivatives thereof. Classification of the following compounds by item is not based on chemical classification. 
In the present invention, the groups of the preferred compounds of Formula (I) shall be shown in the following a) to l).
a) Perylencarboximides of the following formulae: 
in which D is C1-C6alkyl, unsubstituted or halo- or C1-C6alkyl-substituted phenyl, benzyl or phenethyl or B, where B is identical to that described above.
b) Quinacridones of the following formula (III): 
in which R1 and R2 independently of one another are hydrogen, halogen, C1-C24alkyl, C1-C6alkoxy or phenyl, and E is hydrogen or a group of the following formula: 
in which L is any suitable solubilizing group, with the proviso that at least one of the groups E is a group other than hydrogen.
c) Dioxazines of the following formulae: 
in which R3 is hydrogen, halogen or C1-C24alkyl, and E is identical to that described above, 
in which R4, R5 and R6 independently of one another are hydrogen, C1-C4alkyl, C1-C4alkoxy, NECOxe2x80x94C1-C4alkyl, NECO-phenyl or N(E)2, where at least one of R4, R5 and R6 is NECOxe2x80x94C1-C4alkyl, NECO-phenyl or N(E)2, and E is identical to that described above.
d) Isoindolines of the following formulae: 
in which R7 is a group: 
R8 is hydrogen, C1-C24alkyl, benzyl or
a group: 
R9 is hydrogen, E or R7,
R10, R11, R12 and R13 independently of one another are hydrogen,
C1-C24alkyl, C1-C6alkoxy, halogen or trifluoromethyl, and E is identical to that described above.
e) Isoindolinones of the following formulae: 
in which R14 and R15 independently of one another are hydrogen, halogen or C1-C4alkyl, and E is identical to that described above.
f) Anthraquinoid compounds of the following formulae: 
in which R16""s independently of one another are hydrogen or halogen, and E is identical to that described above.
g) Phthalocyanine of the following formula: 
in which M is H2, a divalent metal selected from the group consisting of Cu (II), Zn (II), Fe (II), Ni (II), Ru (II), Rh (II), Pd (II), Pt (II), Mn (II), Mg (II), Be (II), Ca (II), Ba (II), Cd (II), Hg (II), Sn (II), Co (II) and Pb (II), (preferably a divalent metal selected from the group consisting of Cu (II), Zn (II), Fe (II), Ni (II) and Pd (II)), or a divalent metal oxide selected from the group consisting of V(O), Mn(O) and TiO;
T1 is xe2x80x94CHR18xe2x80x94, xe2x80x94COxe2x80x94 or SO2xe2x80x94;
R17 is hydrogen, C1-C6alkyl, xe2x80x94N(E)R18, N(E)2, xe2x80x94NECOR19, xe2x80x94COR19 or a group; 
R18 is hydrogen or C1-C6alkyl;
R19 is C1-C6alkyl;
R20 is hydrogen, halogen, C1-C6alkyl or C1-C6alkoxy;
Z is zero or 1;
y is an integer of 1 to 8, and E is identical to that described above.
h) Pyrrolo[3,4-c]pyrroles of the following formulae: 
in which G1 and G2 independently of one another are any of the following groups, and E is identical to that described above. 
in which R21 and R22 independently of one another are hydrogen, halogen, C1-C24alkyl, C1-C6alkoxy, C1-C18alkylmercapto, C1-C18alkylamino, xe2x80x94CN, xe2x80x94NO2, phenyl, trifluoromethyl, C5-C6cycloalkyl, xe2x80x94Cxe2x95x90Nxe2x80x94(C1-C24alkyl),
a group; 
imidazolyl, pyrazolyl, triazolyl, piperadinyl, pyrrolyl, oxazolyl, benzoxazolyl, benzothiazolyl, benzoimidazolyl, morpholinyl, piperidinyl or pyrrolidinyl;
T2 is xe2x80x94CH2xe2x80x94, xe2x80x94CH(CH3)xe2x80x94, xe2x80x94CH(CH3)2xe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94 or xe2x80x94NR27;
R23 and R24 independently of one another are hydrogen, halogen, C1-C6alkyl, C1-C6alkoxy or xe2x80x94CN;
R25 and R26 independently of one another are hydrogen, halogen or C1-C6alkyl;
R27 is hydrogen or C1-C6alkyl.
i) Quinophthalones of the following formulae: 
in which R28 is hydrogen or Oxe2x80x94E;
R29, R30, R31, and R32 independently of one another are hydrogen, halogen, xe2x80x94COOxe2x80x94C1-C6alkyl or xe2x80x94CONExe2x80x94C1-C6alkyl; and E is identical to that described above.
j) Azo compounds of the following formulae: 
in which R33, R34, R35, R36 and R37 independently of one another are hydrogen, halogen, C1-C6alkyl, C1-C6alkoxy, NO2, acetyl or xe2x80x94SO2NExe2x80x94C1-C6alkyl;
R38 is hydrogen, halogen, C1-C6alkyl or C1-C6alkoxy; and E is identical to that described above.
k) Anthraquinones of the following formulae: 
in which R39 and R40 independently of one another are hydrogen, C1-C12alkyl or C6-C12aryl which is unsubstituted or substituted by halogen, C1-C6alkyl, C1-C6alkoxy, NO2, acetyl, SO2NExe2x80x94C1-C6alkyl or xe2x80x94SO2NE2;
R41 and R42 independently of one another are hydrogen, halogen, C1-C6alkyl, C1-C6alkoxy, NO2, cyano, CONE2, SO2NExe2x80x94C1-C6alkyl or SO2NE2, SO3E, SO3Na or C6-C12aryl which is unsubstituted or substituted by halogen, C1-C6alkyl, C1-C6alkoxy, NO2, acetyl, SO2NExe2x80x94C1-C6alkyl or SO2NE2;
R43 is hydrogen, halogen, NO2, cyano, hydroxyl or C1-C6alkoxy; and B and E are identical to that described above.
l) Indigo derivatives of the following formula: 
in which R44 is hydrogen, halogen, CN, C1-C6alkyl or C1-C6alkoxy, and E is identical to that described above.
To describe in further details, preferred quinacridones are those, wherein in Formula (III) R1 and R2 independently of one another are hydrogen, chlorine or methyl.
Preferred pyrrolo[3,4-c]pyrroles are those, wherein in Formula XIII G1 and G2 are identical and are a group of the following formulae: 
wherein R21 and R22 independently of one another are hydrogen, chlorine, bromine, C1-C4alkyl, C1-C6alkoxy, C1-C16alkylamino, xe2x80x94CN or phenyl;
T2 is xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94SO2xe2x80x94 or xe2x80x94NR27; and
R27 is hydrogen, methyl or ethyl.
Preferred azo compounds are those, wherein in Formulae (XVa) to (XVf) R33, R34, R35, R36 and R37 independently of one another are hydrogen, halogen, methyl, methoxy, NO2, acetyl or SO2NECH3 and R38 is halogen or methoxy.
In the present invention, particularly preferred is any one of the quinacridones of the following formulae: 
wherein E is identical to that described above.
In the present invention, particularly preferred dioxazines are those of the following formula: 
in which R45 and R46 independently of one another are C1-C4alkyl, and E is identical to that described above.
In the present invention, particularly preferred pyrrolopyrroles are those of the following formula: 
in which R47 and R48 independently of one another are hydrogen, methyl, tert-butyl, chlorine, bromine, cyano or phenyl, and E is identical to that described above.
In the present invention, particularly preferred phthalocyanines are those of the Formula (XII) in which M is Cu (II) and R16 is hydrogen or E, and z is 1 and y is 1 to 4 (E is identical to that described above).
In the present invention, particularly preferred isoindolines are those of the following formula: 
in which R49 is C1-C4alkyl, and E is identical to that described above.
In the present invention, particularly preferable indanthrones are those of the following formula: 
in which E is identical to that described above.
In the present invention, particularly preferable azo compounds are those, wherein in Formula (XVa), (XVb), (XVe) or (XVf) described above, R33, R34, R35, R36 and R37 independently of one another are hydrogen, chlorine, methoxy, NO2, acetyl or SO2NECH3, and R38 is halogen or methoxy (where E is identical to that described above).
In the present invention, particularly noteworthy soluble chromophores are those which can be prepared from, for example, the following C. I. Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 83, Pigment Yellow 109, Pigment Yellow 139, Pigment Orange 71, Pigment Orange 73, Pigment Red 122, Pigment Red 185, Pigment Red 202, Pigment Red 254, Pigment Red 255, Pigment Red 264, Pigment Blue 25, Pigment Blue 26, Pigment Blue 60, Pigment Blue 64, Pigment Violet 19, Pigment Violet 29 and Pigment Violet 37.
The compounds of Formulas (I) to (XXI) and the production processes thereof have already been publicly known and are disclosed in, for example, EP648770, EP648817 and EP742556.
In accordance with the present invention, the preferred groups of the solubilizing group xe2x80x94L in Formula (I) shall be shown below: 
in which R50, R51 and R52 independently of one another are C1-C6alkyl;
R53 and R54 independently of one another are C1-C6alkyl, O, S or N(R61)2-interrupted C1-C6alkyl, unsubstituted or halo-, C1-C6alkyl-, C1-C6alkoxy-, NO2xe2x80x94 or cyano-substituted phenyl or biphenylyl;
R55, R56 and R57 independently of one another are hydrogen or C1-C6alkyl;
R58 is hydrogen, C1-C6alkyl or any of the following groups: 
R59 and R60 independently of one another are hydrogen, halogen, C1-C6alkyl, C1-C6alkoxy, cyano, NO2, N(R61)2, unsubstituted or halo-, C1-C6alkyl-, C1-C6alkoxy-, NO2xe2x80x94 or cyano-substituted phenyl;
R61 and R62 are C1-C6alkyl;
R63 is hydrogen or C1-C6alkyl;
R64 is hydrogen, C1-C6alkyl, unsubstituted or C1-C6alkyl-substituted phenyl;
Q is p,q-C2-C6alkylene which is unsubstituted or substituted once or more times by C1-C6alkoxy, C1-C6alkylmercapto or C2-C12dialkylamino (where p and q are different numeric locants);
X is a heteroatom selected from the group consisting of N, O and S, where m is 0 if X is O or S and is 1 if X is N;
L1 and L2 independently of one another are unsubutituted or mono- or poly-C1-C12alkoxy, xe2x80x94C1-C12alkylmercapto, xe2x80x94C2-C24dialkylamino, xe2x80x94C6-C12aryloxy, xe2x80x94C6-C12arylmercapto, xe2x80x94C7-C24alkylarylamino or xe2x80x94C12-C24diarylamino-substituted C1-C6alkyl, or [-(pxe2x80x2,qxe2x80x2-C2-C6alkylene)-Zxe2x80x94]nxe2x80x94C1-C6alkyl (where n is a number of 1 to 1000; pxe2x80x2 and qxe2x80x2 are different numeric locants; each Z independently of the others is a heteroatom comprising oxygen, sulfur or C1-C12alkyl-substituted nitrogen; and all C2-C6alkylenes in the repeating units [xe2x80x94C2-C6alkylene-Zxe2x80x94] can be identical or different);
L1 and L2 can be saturated or mono- to deca-unsaturated, uninterrupted or interrupted in any desired points by from 1 to 10 groups selected from the group consisting of xe2x80x94(Cxe2x95x90O)xe2x80x94 and xe2x80x94C6H4xe2x80x94, and may carry no or 1 to 10 further substituents selected from the group halogen, cyano and NO2.
Preferable are compounds of Formula (I) in which L is C1-C6alkyl or a group: 
in which Q is C2-C4alkylene, and L1 and L2 are [xe2x80x94C2-C12alkylene-Zxe2x80x94]nxe2x80x94C1-C12alkyl or C1-C12alkyl which is substituted once or more times by C1-C12alkoxy, C1-C12alkylmercapto or C2-C24dialkylamino (m and n are as defined above).
Further preferable are compounds of Formula (I) in which L is C4-C5alkyl or the group of the following formula: 
in which Q is C2-C4alkylene, X is oxygen (in this case, m is 0), and L2 is [xe2x80x94C2-C12alkylene-Oxe2x80x94]nxe2x80x94C1-C12alkyl or C1-C12alkyl which is substituted once or more times by C1-C12alkoxy, especially those in which xe2x80x94Qxe2x80x94Xxe2x80x94 is xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94Oxe2x80x94.
Further more preferable pigment precursors of the present invention are compounds of Formula (I) in which the group L is tert-butyl or tert-amyl.
Alkyl and alkylene can be straight-chain, branched, monocyclic and polycyclic.
Specific examples of C1-C12alkyl include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, cyclopentyl, cyclohexyl, n-hexyl, n-octyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl, nonyl, trimethylcyclohexyl, decyl, menthyl, thujyl, bornyl, 1-adamantyl, 2-adamantyl and dodecyl.
Further, if C2-C12alkyl is an unsaturated compound having two or more double bonds such as C2-C12alkenyl, C2-C12alkynyl, C2-C12alkapolyenyl and C2-C12alkapolyinyl, specific examples of this C1-C12alkyl are vinyl, allyl, 2-propene-yl, 2-butene-1-yl, 3-butene-1-yl, 1,3-butadiene-2-yl, 2-cyclobutene-1-yl, 2-pentene-1-yl, 3-pentene-2-yl, 2-methyl-1-butene-3-yl, 2-methyl-3-butene-2-yl, 3-methyl-2-butene-1-yl, 1,4-pentadiene-3-yl, 2-cyclopentene-1-yl, 2-cyclohexene-1-yl, 3-cyclohexene-1-yl, 2,4-cyclohexadiene-1-yl, 1-p-menthene-8-yl, 4(10)-thujen-10-yl, 2-norbornene-1-yl, 2,5-norbornadiene-1-yl, 7,7-dimethyl-2,4-norcaradiene, and various isomers such as hexynyl, octenyl, nonenyl, decenyl and dodecenyl.
Specific examples of C2-C4alkylene are 1,2-ethylene, 1,2-propylene, 1,3-propylene, 1,2-butylene, 1,3-butylene, 2,3-butylene, 1,4-butylene and 2-methyl-1,2-propylene.
Specific examples of C5-C12alkylene are various isomers of pentylene, hexylene, octylene, decylene and dodecylene.
C1-C12alkoxy is Oxe2x80x94C1-C12alkyl, preferably Oxe2x80x94C1-C4alkyl.
C6-C12 aryloxy is Oxe2x80x94C6-C12aryl, and specific examples thereof are phenoxy or naphthoxy, preferably phenoxy.
C6-C12 arylmercapto is Sxe2x80x94C1-C12aryl, and specific examples thereof are phenylmercapto and naphthylmercapto, preferably phenylmercapto.
C2-C24dialkylamino is N(alkyl1)(alkyl2), where the sum of the carbon atoms in the two groups alkyl1 and alkyl2 is from 2 to 24, preferably N(C1-C4alkyl)-C1-C4alkyl.
C7-C24alkylarylamino is N(alkyl1)(aryl2), where the sum of the carbon atoms in the two groups alkyl1 and aryl2 is from 7 to 24, for example methylphenylamino, ethylnaphthylamino or butylphenanthrylamino, preferably methylphenylamino or ethylphenylamino.
C12-C24diarylamino is N(aryl1)(aryl2), where the sum of the carbon atoms in the two groups aryl1 and aryl2 is from 12 to 24, for example diphenylamino or phenylnaphthylamino, preferably diphenylamino.
Halogen is chlorine, bromine, fluorine or iodine, preferably fluorine or chlorine.
n is preferably a number from 1 to 100, with particular preference a number from 2 to 12.
Used as the organic solvent of the present invention are all of aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, amides, nitrites, nitro compounds, N-heterocyclic compounds, ethers, ketones and esters as long as they are publicly known and available in the market and can dissolve the compounds of Formula (I) described above. Water can be used as well if appropiate. These solvents have preferably a boiling point of 40 to 300xc2x0 C.
To describe the solubility, the solvents which can dissolve the compound (I) in a proportion of 5% by weight or more, preferably 10% by weight or more are preferred in terms of a density in drawn lines of the lead. Specific examples thereof are methanol, ethanol, isopropanol, n-butanol, benzyl alcohol, diethyl ether, 1-acetoxy-2-ethoxyethanol, acetone, methyl ethyl ketone, cyclopentanone, butyrolactone, 1-methoxy-2-propanol, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methoxyethanol, 2-methoxy-propyl acetate, ethyl acetate, butyl acetate, isopropyl laurate, methyl methacrylate, tetrahydrofuran, dioxane, acetonitrile, benzonitrile, nitrobenzene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, pyridine, picoline, quinoline, dichloromethane, chloroform, methylcyclohexane, benzene, toluene, xylene, diisopropylnaphthalene, anisole and chlorobenzene. It is a matter of course that these solvents can be used in a mixture thereof.
In the present invention, a method for filling a porous sintered lead with a solution of the compound which is the pigment precursor of Formula (I) described above comprises dipping the porous sintered lead into the solution described above to fill the pores thereof with the solution, if necessary, under conditions of heating and applying pressure or reducing pressure.
Then, the organic solvent is removed by drying, and the lead is heated at a temperature of 100 to 250xc2x0 C., preferably 150 to 200xc2x0 C. and particularly preferably 160 to 200xc2x0 C. which is optimum to the respective pigment precursors to convert the compound of Formula (I) described above into an organic pigment.
A catalyst such as, for example, an acid can be used if appropiate in order to lower the pigmenting temperature.
Heating time for pigmenting is different according to the heating temperature, a size and a shape of the lead pores and other conditions, and therefore it can not generally be defined. It is approximately several seconds to several hours, preferably 1 to 30 minutes.
Further, dipping and heating may be repeated in order to increase a density in the drawn lines.
The compounds which are the pigment precursors of Formula (I) can be mixed and dissolved in a solvent and heated to obtain an optional mixed color.
The lead obtained after the compound of Formula (I) described above is converted into a pigment can be impregnated, if necessary, with a lubricant such as oil, a UV absorber, a light stabilizer and an antistatic agent for the purpose of elevating stability with the passage of time and a writing feeling.
In the process for producing a sintered color pencil lead of the present invention thus constituted, the following effects (1) to (3) are provided.
(1) The compound of Formula (I) described above can be dissolved in an organic solvent in a high concentration, and a solution thereof has a low viscosity, so that a lead having such a small pore diameter as in the present invention can be impregnated with said solution equally to or more than a dye ink. Accordingly, the pores of the lead can readily be filled with the pigment in an amount sufficient for obtaining a high density in the drawn lines. Further, it is a solution of an organic solvent, and therefore it does not deteriorate the lead comprising ceramics, clay and the like.
(2) A plurality of the compounds of Formula (I) described above can be blended in an optional proportion and dissolved in a specific organic solvent, and multicoloring of the lead can easily be achieved. Further, the organic pigment obtained after heating the compound described above is stable with the passage of time, and therefore the sintered color pencil lead which has a vivid coloring property and a sufficiently high density in the drawn lines and which is excellent in stability with the passage of time such as light fastness can be obtained according to the present invention.
(3) The colorant for the sintered color pencil lead of the present invention is a solid pigment at the final stage and is not adhered onto a paper face unlike the conventional dye inks, and therefore the color pencil lead having an excellent erasability with an eraser is obtained.